1. Title of the Invention
The present invention relates to an intake air flow regulating method for regulating intake air flow for motor vehicle internal combustion engines, particularly to a method for regulating intake air flow for internal combustion engines for motor vehicles when running under the engine with idle speed controller.
2. Description of the Prior Art
As is known, the idle speed control, which is hereinafter referred to as ISC, for a motor vehicle engine is a method for controlling intake air flow, wherein a set or target speed of rotation, when the engine is in the indling condition is memorized in a memory, engine conditions are detected by each sensor which produces each detected signal and changes an opening of a bypass path, through which air is sent to a combustion chamber bypassing a throttle valve so as to equalize the speed of engine rotaions to the set speed of rotations.
Heretofore, as mentioned above, when an internal combustion engine wherein ISC is performed is not in the idling condition, for example when the engine is in a running condition, an idle speed control valve (ISCV) for regulating the opening of the bypass path is maintained constant in the opening. This opening condition is determind by a learning value of the opening of ISCV, which is finally set when a feedback control for ISC is being performed. The learning value is an actual opening value which continues to be memorized as long as a feedback control for ISC is being performed.
An idle switch connected to the throttle valve and detecting a fully closed condition of the thrrottle valve itself is difficult to turn ON at the time the throttle valve is completely or fully closed due to the nature of its construction. For this reason, the idle switch has been already turned ON in the condition where the throttle valve is in an opened condition in some degree. In this case, when a driver is trying to make a steady running at relatively low speed, the normal or steady running can be performed without almost operating an accelerator, i.e. without opening the throttle valve so much since ISCV mention above is in the open condition with the learning opening value.
In the steady running, if the throttle valve opening is too small, the idle switch may become turned ON due to the nature of the idle switch even when the opening of the throttle valve is not zero. When the idle switch is turn ON, a control unit which controls the ignition timing of the internal combustion engine decides that the engine is whether in the condition of idling or in the condition of deceleration, with the idle switch being turned ON and it changes the ignition timing to that set in the condition of no load, that is, the ignition timing for an idling engine. The angle of this ignition timing in this case, is more delayed during running and therefore it can no longer coincides with the ignition timing necessary for the steady running, with the result that the driveability as well as fuel consumption rate are deteriorated.
FIG. 1 shows a timing chart for controlling the operation of the ignition timing. The waveform (a) indicates the change in car speed as time is elapsed, (b) indicates the change in the time between the idling condition of the internal combustion engine and a time the engine is in a condition other than the former condition, (c) indicates the change in the time between the turning ON and OFF of the idle switch, (d) indicates the change in the time between the ignition timing for the engine idling engine and the ignition timing other than the former period, (e) indicates the change in the duty D of a signal for controlling the opening of ISCV as the time elapsed.
First of all, the waveform (b) shows that before the time T1, the engine is in the idling condition, the car speed is zero, and the idle switch is ON while the ignition timing is set for the idling engine, and the duty D is calculated according to a feedback control, and the opening of ISCV is automatically controlled in accordance with the result of the calculation.
At the timing T1, the accelerator is operated and a clutch is engaged so as to change the engine from the engine idling condition. In this case, when the car is started, the idle switch is turned OFF. As a result, the ignition timing is changed from that set when the engine is idling to that for controlling the running with a load, and the duty D is set to the learning value DG including the final duty of the feedback control, while the opening area of ISCV is fixed to the area corresponding to the learning value.
Then, in the acceleration and in the steady running thereafter, no more change occurs to the idle switch, the ignition timing and the duty D. At the timing T2, the accelerator is released and the operation for lowering the car speed is carried out by operating the break pedal or the engine break. In this case, the idle switch is turned ON until the timing T3 when the accelerator is operated again. As a result, the ignition timing is changed to the ignition timing set for the idling engine. However, after the timing T3, as the accelerator is pressed to some degree for changing to the steady running of relatively high speed, then the timing condition of idle switch, engine, ignition timing become the same as before the timing T2.
When the car speed is lowered again at the timing T4, the idle switch is turned ON, similar to the condition at the timing T2 and the ignition timing in the engine of idling is performed. However, although the accelerator pedal is operated in order to make the relatively low speed steady running from the timing T5, the steady running in this case is the one with a small load. Accordingly, almost to pressing of the accelerator pedal is required and the idle switch remains turned ON.
As a result, it follows that ignition timing of the engine in an idling condition continues to another time period although the ignition timing is for the steady running. Namely, the steady running from the time period between T5 and T6 during which the brake is operated, is the running due to the ignition timing for the idling engine, which results in the degradation of the drivability and the fuel consumption rate. In this case, FIG. 1 shows that during the time period between T6 and T7, that deceleration is performed and after the timing T7, the engine becomes in a condition of idling.